Normalize build, CI/CD, and centralized versioning

[uniblab]

Summary

Normalizes Icod.UtilLinux to the canonical build and release pattern maintained in uniblab/.github, preserves the current 1.0.1 repository version, and adds the repository-level utillinux router/.NET tool package.

Versioning

• adds root Directory.Build.props as the single version source;
• centralizes VersionPrefix, Version, PackageVersion, AssemblyVersion, and FileVersion at 1.0.1;
• removes duplicated <Version>1.0.1</Version> from kill and renice.

Router and package topology

• adds utillinux/Icod.UtilLinux.Router.csproj;
• routes utillinux kill [args...] and utillinux renice [args...] directly in-process;
• adds router-level --help and --version;
• adds Router.Tests, including -V dry-run dispatch for both commands;
• makes kill and renice non-packable while retaining them as standalone executable projects;
• makes Icod.UtilLinux.Tools the sole NuGet/.NET tool package with installed command utillinux;
• validates exactly one package with package ID Icod.UtilLinux.Tools in local builds, PR CI, distribution validation, and release packaging;
• keeps utillinux, kill, and renice available to RID release archives.

Local build tooling

• normalizes build.cmd and build.sh;
• adds packaging/RepositoryTools.psm1 and metadata/build/package/distribution/archive helpers;
• local wrappers use Debug and support clean/restore/build/test/pack/validate stages.

CI/CD

Replaces the legacy PR/main workflows with the canonical lifecycle:

• pull-request.yaml: Staging on Windows, Linux, and macOS, with Linux exact-package validation;
• main.yaml: Release distribution validation on Windows/Linux/macOS x64 and ARM64;
• distribution-validation.yaml: manually dispatched Debug/Staging/Release six-runner validation;
• release.yaml: v<semver> package selection/publication, six RID archives, checksums, and GitHub Release creation.

The legacy pr-build-and-test.yaml and push-main.yaml workflows are removed.

Documentation

• adds canonical PR/main badges;
• documents centralized versioning and the normalized lifecycle;
• documents installation and use of Icod.UtilLinux.Tools / utillinux;
• adds packaging/README.md.

No kill or renice command semantics are intentionally changed.